1. Field of the Invention
The present invention relates to linear actuator technology and more particularly, to a safety linear actuator assembly, which comprises an actuator comprising a hollow holder frame, a gear set mounted in the hollow holder frame, a transmission mechanism having a lead screw inserted into the hollow holder frame and coupled to the gear set and bearing holders mounted on a stem at one end of the lead screw and disposed inside the hollow holder frame to hold a respective thrust bearing on the stem of the lead screw, and a retaining ring fastened to a locating groove at the stem of the lead screw and positioned in the bearing holder for stopping the lead screw from axial displacement to ensure a high level of operational safety in case the stem of the lead screw breaks accidentally.
2. Description of the Related Art
Many different types of linear actuators with different mechanical and transmission designs are known for use in medical or home beds, massage chairs, fitness machines, rehabilitation equipments, door/window openers, lifting mechanisms and many other electrically controllable displacement devices for elevation or angular position adjustment. During the operation of the motor in a conventional linear actuator, a worm/driving shaft is driven by the motor to rotate a worm gear or gear set and a lead screw, causing movement of a sliding block along the lead screw, and thus, a linked retractable tube or bracket of an external apparatus is moved to achieve elevation or angular position adjustment.
However, during the operation of the worm/driving shaft to rotate the worm gear or gear set and the connected lead screw in moving the linked retractable tube or bracket of the external apparatus, the torsional force thus generated is large. When stopping the actuator, the load can cause the lead screw to rotate in the reversed direction, and the retractable tube (or external apparatus) can fall suddenly, causing an accident. In order to prevent this problem, a brake can be added to the actuator to lock the actuator when it is stopped. Further, during rotation of the lead screw of the actuator, the pin that is fastened to a pin hole at one end of the lead screw to hold a cushion ring between two thrust bearings in respective hearing holders inside a hollow holder frame of the actuator can prohibit the lead screw from axial displacement relative to the hollow holder frame. However, if the lead screw receives a large torsional load and a high impact, a stress concentration can occur at the area of the lead screw around the pin and the lead screw can break and escape out of the hollow holder frame, threatening operational safety. An improvement in this regard is desired.